Manufacture of target for use in magnetron sputtering of nickel and like magnetic metals for forming metallization films having consistent uniformity through life

ABSTRACT

Improved targets for use in DC magnetron sputtering of nickel or like ferromagnetic face-centered cubic (FCC) metals are disclosed for forming metallization films having effective edge-to-edge deposition uniformity of 5% (3σ) or better. Such targets may be characterized as having: (a) a homogeneous texture mix that is at least 20% of a &lt;200&gt; texture content and less than 50% of a &lt;111&gt;texture content, (b) an initial pass-through flux factor (%PTF) of about 30% or greater; and(c) a homogeneous grain size of about 200 μm or less.

This application is a continuation of Ser. No. 09/054,067, filed Apr. 2,1998. The disclosure of said application is incorporated herein byreference.

BACKGROUND

1. Field of the Invention

The invention relates generally to physical vapor deposition (PVD) ofmetal films.

The invention relates more specifically to DC magnetron sputtering offerromagnetic metals such as nickel (Ni) onto semiconductor substratesand the like for forming metallization such as found in theelectrically-conductive interconnect layers of modern integratedcircuits.

2a. Cross Reference to Related Patents

The following U.S. patent(s) is/are assigned to the assignee of thepresent application, and its/their disclosures is/are incorporatedherein by reference:

(A) U.S. Pat. No. 5,242,566 issued Sep. 7, 1993 to N. Parker;

(B) U.S. Pat. No. 5,320,728 issued Jun. 14, 1994 to A. Tepman; and

(C) U.S. Pat. No. 5,540,821 issued Jul. 30, 1996 to A. Tepman.

2b. Cross Reference to Related Other Publications

The following publication(s) is/are cited here for purposes ofreference:

(a) Y. M. Ahn et al (Samsung Electronics, Korea), STUDY ONMAGNETO-OPTICAL TbFeCo THIN FILMS MAGNETRON-SPUTTERED FROM TARGETS WITHLOW AND HIGH PERMEABILITIES, Intermag 97 conference of April 1997; and

(b) Y. Nakamura et al (Japan Energy Corp.), INFLUENCE OF PERMEABILITY ONCo TARGET USAGE, pp. 651-656, Proc. of 4^(th) ISSP (Kanazawa, Japan1997), Jun. 4-6, 1997.

3. Description of the Related Art

The electrically-conductive interconnect layers of modern integratedcircuits (IC) are generally of very fine pitch (e.g., 10 microns orless) and high density (e.g., hundreds of lines per square millimeter).

If there is nonuniformity of thickness or nonhomogeneity in otherattributes of the precursor metal films that ultimately form themetallic interconnect layers of an IC, such lack of uniformity can leadto out-of-tolerance topographies and improper semiconductor fabrication.The latter can be detrimental to the operational integrity of theultimately-formed IC. As such it is desirable to form metal films withgood uniformity across each of mass-produced wafers.

The metal films of integrated circuits may be formed by physical vapordeposition (PVD). One low cost approach uses a DC magnetron sputteringapparatus such as the Endura™ system available from Applied MaterialsInc. of California for sputtering metals onto semiconductor wafers orother like workpieces.

Aluminum (Al) is the most common metal that is deposited by DC magnetronPVD sputtering. Aluminum can be characterized as a polycrystalline,electrically conductive material whose crystals have a face-centeredcubic (FCC) structure. One of the characteristics of Al is that it is anessentially nonmagnetic material. (Al may be considered paramagneticthough.)

Recently it has been proposed that magnetic metals such as nickel (Ni)may also be deposited using the Endura™ or like DC magnetron PVDsystems.

Because nickel (Ni) is a ferromagnetic material, it presents newproblems that had not been earlier posed by nonmagnetic materials suchas aluminum. In particular, magnetic flux fields generated within the DCmagnetron PVD system may be significantly altered due to shunting orshort circuiting of the magnetic flux through the magneticallyconductive material of ferromagnetic (e.g., Ni) targets. Such shuntingcan make it difficult to strike a plasma or sustain a generally-uniformplasma over time and can lead to associated problems such as nonuniformdeposition. There is a question as to whether ferromagnetic targets ofpractical thicknesses (e.g., 3 millimeters or greater) can be used forsputtering with a DC magnetron PVD system.

The present inventors have through experimentation, isolated a number ofphysical attributes of ferromagnetic targets (e.g., nickel targets) thatcollectively correlate with how uniform the deposited film is across thesubstrate and how efficiently the material of the target is used. Thesecollective correlations are disclosed herein together with designs forimproved ferromagnetic targets.

SUMMARY OF THE INVENTION

It has been determined that fairly stable plasmas can be struck andsustained in DC_magnetron PVD systems even if ferromagnetic targets areused, and even if the targets have a thickness of as much as 3 mm ormore.

Three attributes of nickel-based targets have been found to collectivelycorrelate with uniform deposition thickness. They are in order ofimportance (with no one factor being dominant by itself): (1) the mix ofcrystallographic textures in the target, (2) the target's initialpass-through flux factor (%PTF), and (3) the maximum metal grain size inthe target.

More particularly it has been found that; where the commercially usefullife of nickel targets is limited by cross-workpiece depositionuniformity, an improvement can be obtained in the form of: (1) betterdeposition uniformity through the commercially useful life of nickeltargets (e.g., a useful life of at least 60 Kilowatt Hours {kWHrs}),and/or (2) a longer commercially useful life for each nickel target inview of given limit on acceptable nonuniformity (e.g., cross-waferresistivity variation of about 5% or less (at 3σ) over target life).

Such improvement in target longevity and/or deposition uniformity may beobtained first by providing, in ferromagnetic targets that have athickness of as much as 3 mm or more: an average (with per-samplepointrestrictions), and more preferably, a homogeneous crystalline texturemix that is at least 20% of the <200> oriented texture. More preferably,the texture mix should at the same time be less than about 50% of the<111> oriented texture. Even more preferably, an average, and morepreferably, a homogeneous texture mix should be provided that is atleast 32% <200> texture, while further keeping at less than about 10%the <111> oriented texture. Yet more preferably, an average, and morepreferably, a homogeneous texture mix should be provided that is atleast 35% <200> texture, while further (optionally) keeping at less than9% the <111> oriented texture. Yet more preferably, the latterhomogeneous texture mix should further keep at less than 30% the <113>oriented texture. The remainder of the homogeneous texture mix can be ofthe <220> texture.

The above-mentioned average with per-sample-point restrictions may bedetermined for each value of texture in the texture mix by averagingover a multi-point symmetric pattern such as for example a star havingfour outer points and one central point. Star patterns with greaternumbers of points can, of course, be alternatively used. The phrase,“with per-sample-point restrictions”, indicates that each of the samplepoints participating in the average must further comply with a limiteddeviation such as being plus or minus 10% of the calculated average. Byway of a more specific example, calling for a 20% average content of the<200> oriented texture with a per-sample-point restriction of +/−10%means that anyone of the sample points can be as low as 18% in contentof the <200> oriented texture or as high as 22% in content of the <200>oriented texture, so long as the unweighted average is still 20%. In oneembodiment, each of the above average specifications for each given typeof oriented texture carries with it a per-sample-point restriction(PSPR) of +/−10%. In more tightly specified, second embodiment, each ofthe above average specifications for each given type of oriented texturecarries with it a per-sample-point restriction of +/−5%. Otherrestriction values may be used provided they are no tighter than themargin of error for per-sample-point measurements and not so loose as tomake the average value meaningless with respect to physical consequences(e.g., a per-sample-point restriction of greater than about +/−50%).

Improvement in target longevity and/or through-life depositionuniformity may be further obtained for such thick ferromagnetic targets(e.g. 3 mm or greater thickness) by simultaneously providing (for anyone of the texture mixtures specified immediately above) an initialthrough-target pass-through flux factor (%PTF) that is at least highenough to initially strike a plasma and preferably a higher %PTF. Aninitial %PTF of about 30% or greater on average with a per-sample-pointrestriction of between +/−10% and +/−5% across the active (sputtering)portion of the target has been found workable for a permanent drivingmagnet of about 400 to 500 Gauss. More preferably, the initial %PTF ofabout 30% or greater should be found homogeneously across the active(sputtering) portion of the target rather than merely on a 5-point orother average.

Improvement in target longevity and/or through-life depositionuniformity may be further obtained by simultaneously providing with saidtexture mixtures and/or said initial %PTF, an average, and morepreferably, a homogeneous grain size in the target of about 200μm (200microns) or less, where the grain size value is one provided by theE1172 measurement procedure of ASTM (American Standard Test ofMaterials) or by a substantially equivalent measurement method for grainsize that takes into account grain size at the center and active edge ofthe target. More preferably, a grain size of about 150 μm or less shouldbe provided. Even more preferably, a grain size of about 100 μm or lessshould be provided. The per-sample-point restriction (PSPR) for theaverage value of grain size should no more than about +/−10 μm and morepreferably, no more than about +/−5 μm and even more preferably, no morethan about +/−3 μm. By way of example, the above-mentioned preferredvalues for average grain size may be more specifically defined accordingusing the following per-sample-point restrictions: 200 μm AVG +/−10 μmPSP; or 150 μm AVG +/−5 μm PSP; or 100 μm AVG +/−3μm PSP.

Improved uniformity through the useful life of for such thickferromagnetic targets (e.g., 3 mm or thicker nickel targets) may be yetbetter obtained by simultaneously providing all three of theabove-described, preferred ranges for average or homogeneous texturemix, initial %PTF, and grain size.

A DC_magnetron PVD system in accordance with the invention comprises aferromagnetic target having at least two of the following threecharacteristics: (a) a homogeneous texture mix that is at least 20% ofthe <200> oriented texture, (b) a homogeneous across-the-target, initialpass-through flux factor (PTF) of about 30% or greater, and (c) ahomogeneous grain size of less than about 150 μm.

A method for operating a DC_magnetron PVD system in accordance with theinvention comprises the step of: (a) installing a ferromagnetic targethaving at least two of the following 3 characteristics: (a.1) ahomogeneous texture mix that is at least 20% of the <200> orientedtexture, (a.2) a homogeneous across-the-target, initial pass-throughflux factor of 30% or greater, and (a.3) a homogeneous grain size ofless than 150 μm; and further comprises the step of: (b) adjusting thetarget to wafer spacing automatically during useful target operation soas to optimize uniformity due to target-to-workpiece spacing.

A target qualification method in accordance with the invention comprisesthe steps of: (a) testing supplied samples of respective lots offerromagnetic targets for at least two of the following characteristics:(a.1) a homogeneous or average texture mix that is at least 20% of the<200> oriented texture, (a.2) a homogeneous or averageacross-the-target, pass-through flux factor of 30% or greater, and (a.3)an average grain size of less than about 150 μm AVG +/−5 μm PSP; andfurther comprises the step of: (b) proscribing use as targets forDC_magnetron sputtering operations where resistivity uniformityvariation of no more than 5% (3σ) is desired, the targets from lotswhose samples do not pass said at least two testing steps.

Other aspects of the invention will become apparent from the belowdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The below detailed description makes reference to the accompanyingdrawings, in which:

FIG. 1 is a schematic diagram of a DC_magnetron PVD system;

FIG. 2A shows before and after cross sections for demonstrating atypical erosion profile for a nonmagnetic target (e.g., aluminum);

FIG. 2B shows before and after cross sections for demonstrating atypical erosion profile for a ferro-magnetic target (e.g., nickel);

FIG. 3A contains plots for comparing relative erosion profiles of aconventional aluminum target and a first nickel target designated asSample ‘A’;

FIG. 3B is a plot showing over-target-life deterioration of depositionuniformity for the first nickel target (Sample ‘A’);

FIG. 4A shows a plot of through-life uniformity of across-the-waferdeposition for a second nickel target (Sample ‘B’);

FIG. 4B plots target-to-wafer spacing curves relative toacross-the-wafer deposition uniformity for the second nickel target(Sample ‘B’);

FIG. 4C is a photograph showing sand dune structures on the surface ofthe second nickel target (Sample ‘B’) after sputtering;

FIG. 5A shows a plot of through-life uniformity of across-the-waferdeposition for a third nickel target (Sample ‘C’);

FIG. 5B plots target-to-wafer spacing curves relative toacross-the-wafer deposition uniformity for the third nickel target(Sample ‘C’);

FIG. 6A plots through-life, across-the-wafer deposition uniformity for afourth nickel target (Sample ‘D1’) when autospacing is invoked ormimicked;

FIG. 6B plots target-to-wafer spacing curves relative toacross-the-wafer deposition uniformity for the fourth nickel target(Sample D1);

FIG. 7A plots through-life, across-the-wafer deposition uniformity for afifth nickel target (Sample D2) when autospacing is invoked or mimicked;and

FIG. 7B plots target-to-wafer spacing curves relative toacross-the-wafer deposition uniformity for the fifth nickel target(Sample D2).

DETAILED DESCRIPTION

FIG. 1 shows a schematic diagram of a DC sputtering magnetron system100. In this schematic, the x-axis extends down while the y-axis extendslaterally. The x-direction corresponds to a <200> FCC crystalorientation. The y-direction corresponds to a <020> Face Centered Cubiccrystal orientation and is understood to alternatively represent a <002>FCC crystal orientation or any orientation that is intermediate alongthe yz plane between <020> and <002>, such as <022 >.

In system 100, a magnet 110 (or a set of magnets, which can includemoving and/or stationary permanent and/or electromagnets) is positionedover a portion of target 120. Typically, a spacing 118 between themagnet and target is provided by nonmagnetic shims or other nonmagneticspacing means.

The target 120 is positioned over and spaced apart from a workpiece 150.A spacing 128, between the target and workpiece is referred to as theT/W spacing. This T/W spacing 128 may adjusted manually orautomatically, such as by the illustrated stepper motor 105 which isarranged to move the combination of target 120 and magnet 110 up anddown. The mechanical connection between motor 105 and the magnet/targetcombination 110/120 is represented by dashed line 104 and can be a leadscrew or other means for converting the output of motor 105 intoappropriate movement of the magnet/target combination. The direction andspeed of motor 105 may be controlled by a programmable computer 106. T/Wspacing 128 may be adjusted automatically by computer 106 formaintaining such spacing 128 to optimize uniformity over life inaccordance with the disclosure of the above-cited U.S. Pat. No.5,540,821 through the operational lifetime of the target 120. Suchautomatic adjusting of T/W spacing 128 is referred to herein as‘auto-spacing’.

Computer 106 may include a real-time clock 107 for keeping track of theaccumulated sputtering time. Computer 106 may further include powermeasuring means for keeping track of the accumulated product ofsputtering time times power (or of other like target deteriorationparameters) of each target that is installed into system 100. In oneembodiment, clock 107 keeps track of how long computer-controllableswitch 125 is closed and the computer 106 calculates the amount of workdone by target 120 as a function of applied power (voltage timescurrent) integrated over time of switch closure.

The magnet 110 produces a flux field 115 of a given intensity. At leasta portion 116, if not all of the produced flux 115 should pass throughthe target into the space 128 between the target 120 and the workpiece150. If the target 120 contains ferromagnetic material such as nickel ora magnetic alloy of nickel (e.g., Ni_(1−x)Si_(x), where x≦1%), a portion114 of the produced flux 115 may shunt through the target in a y-zdirection rather than passing through into the space 128 between thetarget 120 and the workpiece 150. The relative amount of shunting(114/115) generally decreases as target thickness decreases. Therelative amount of shunting (114/115) can also depend on other factorsas will be seen. If, in contrast, the target 120 is primarily composedof a nonmagnetic material such as aluminum, there will be essentially noshunting and most if not all of the produced flux 115 passes aspassed-through flux 116 into the T/W spacing 128.

The intensity and spatial extent of the passed-through magnetic flux 116plays an important role in generating a sputter-causing plasma 160 andin determining uniformity of deposition as will be explained shortly.

The target 120 within the DC_magnetron PVD system is electricallyconductive and is composed of a to-be-sputtered material. Theto-be-sputtered material can include a variety of metals such asnonmagnetic aluminum in conventional systems and ferromagnetic metalssuch as nickel in systems in accordance with the present invention.

A plasma 160 is created and sustained in the space 128 between thetarget and the workpiece. Once created (struck) and sustained, theplasma bombards a sputtering surface 120 a of the target with energizedparticles. This bombardment causes small particles of theto-be-sputtered material to break away from the target's sputteringsurface 120 a and to move to the workpiece 150 for deposition on theworkpiece. As a result, the target erodes over time (that is, targetthickness tends to decrease with usage) and deposition films are formedon a stream of workpieces 150 that pass under the target.

The initial target 120 is typically of a smooth symmetrical form such asa circular disk with a planar work surface, but may have various bendsor other features such as shown for adaptively fitting into a specificDC₁₃magnetron PVD system and for producing specific distributions ofelectrical field intensity, magnetic field intensity, and gas flow inaccordance with design specifics of the receiving DC_magnetron PVDsystem. Each workpiece 150 also generally has a smooth symmetrical formsuch as a circular disk with a planar work surface at the start ofdeposition. One example is a pre-planarized semiconductor wafer.Typically, one target is used for depositing films 155 on manyworkpieces (e.g., at least 20 or more wafers).

The target 120 is typically structured for removable insertion into thecorresponding DC_magnetron PVD system 100. Used targets are periodicallyreplaced with a new targets given that the PVD process erodes away theto-be-deposited material of each target over time. The useful depositionlife of the target, which life is typically measured in terms ofkiloWattHours or in terms of total deposited, film thickness, isreferred to as the target's useful life span.

A switching means such as computer-controlled switch 125 may be providedfor selectively connecting the target 120 to a relatively negativevoltage source 127. (The voltage and/or current of source 127 may alsobe computer-controlled.) In general, the negative voltage source 127provides a DC cathode voltage in the range of about −470V to −530Vrelative to the potential on an opposed anode (ground or GND in theillustrated example). Higher voltages may be used for initially striking(igniting) the plasma 160. The specific cathode voltage varies accordingto design. When the switching means 125 is closed to connect the target120 with negative voltage source 127, the target can act as a source ofparticles such as 145 (e⁻) and 149 (Ni) which are discussed below. Thetarget is also sometimes referred to as the cathode.

A tubular gas-containment shield 130, usually of cylindrical shape, isprovided below and spaced apart from the target 120. Shield 130 iselectrically conductive and is generally coupled to ground (GND) or toanother relatively positive reference voltage so as to define anelectrical field between the target 120 and the shield. Shield 130 has aplurality of apertures 132 (only one shown) defined through it foradmitting a supplied flow of plasma-forming gas 130 such as argon (Ar)from the exterior of the shield 130 into its interior.

A workpiece-supporting chuck 151 is further provided centrally below andspaced apart from the target 120, usually within the interior of theshield 130. Chuck 151 is electrically conductive and is generally alsocoupled to ground (GND) or to another relatively positive referencevoltage so as to define a further electrical field between the target120 and the chuck.

Workpiece 150 is a replaceable item such as a planar semiconductor waferand is supported on the chuck centrally below the target 120. Workpiece150 originally consists of a substrate 152 having an exposed top surface152 a. As PVD sputtering proceeds, a metal film 155 having a top surface155 a builds up on the substrate 152. In many instances it is desirablethat the build up or deposition of the metal film 155 be uniform acrossthe entire top surface 152 a of the substrate, from edge-to-edge. But asexplained shortly herein, changes to the target 120 which develop overthe useful life of the target can begin to interfere with homogeneousdeposition. When the target can no longer provide a desired uniformityof edge-to-edge thickness of deposition for workpieces (e.g., wafers)150 moving through the system 100, the useful life span of the target isdeemed to be at its end.

The term ‘edge-to-edge’ as used herein does not require measurement fromthe absolute edge of the workpiece and allows for a peripheral exclusionzone such as commonly found in commercial production of semiconductorwafers. Typically, the exclusion zone of semiconductor wafers isapproximately 3 mm for wafers of 150 mm (or 200 mm) diameter therebygiving an effective diameter of 144 mm (or 194 mm, respectively).

DC magnetron operation initiates as follows. When switching means 125 isclosed, initial electric fields are produced between the target 120 andthe shield 130 and the chuck 151. The plasma-creating gas 130 (e.g., Ar)is introduced. The illustrated assembly of FIG. 1 is usually housed in alow pressure chamber 105 (partially shown) that maintains an internalpressure in the range of about 2 mTorr to 5 mTorr or lower. An exhaustpump (not shown) may be provided to remove old gas and thereby allowreplacement with new gas 130.

Some of the supplied gas 130 that enters the interior of shield 130disassociates into positively charged ions (Ar⁺) and negatively chargedions (Ar⁻) when subjected to ambient photo electrons. The negativelycharged ions (Ar⁻) preferably move toward the positively-charged shield130 while the positively charged ions (Ar⁺)move toward thenegatively-charged target 120.

One so-generated positive ion is shown at 141. Due to electrostaticattraction, ion 141 (Ar⁺) accelerates towards and collides with thebottom surface 120 a of the negatively-charged target at a firstcollision point, say 142. The point of collision is denoted with a star(“*”). This initial collision generally induces the emission of a firstelectron (e⁻) 145 from cathode 120. (A particle of target material (Ni)may also be dislodged by the initial collision 142 but is not shown forsake of avoiding illustrative clutter.) The emitted electron 145 driftsdown towards the more positive chuck 151. However, the passed-throughflux 116 of magnet 110 (if strong enough) confines the moving electron145 to a spiraling trajectory as indicated at 146. This spiralingtrajectory 146 moves the electron 145 through the feed gas (Ar₂) withinthe interior of the shield 130. Eventually the magnetically-confinedelectron 145 collides with a molecule of the feed gas 130. This secondcollision disassociates the Ar₂ molecule and produces another positivelycharged ion 147 (Ar⁺) which accelerates towards and collides with thebottom surface 120 a of the target. This new collision 148 produces yetanother electron like 145.

Eventually, a chain reaction is established leading to the creation of asustained plasma 160 within the interior of the gas-containment shield130. Plasma 160 is charged positive relative to the cathode 120 andbegins to act like a floating anode. This changes the electric fielddistribution within the DC_magnetron PVD system 100. At some point theelectric field distribution stabilizes into a long term steady statesuch that plasma 160 is distributed in the space between target 120 andworkpiece 150 and confined by the passed-through flux 116 of magnet 110.

The ignited and sustained plasma 160 acts as a source of bombardmentparticles such as 147.

It should be appreciated that the intensity and spatial extent of thepassed-through flux 116 determines the behavior of spiraling electronssuch as 145 and thereby determines characteristics of the plasma 160.The intensity and spatial extent of the passed-through flux 116 shouldbe adjusted to fall within a workable range. If the passed-through flux116 is too weak, it may be insufficient to provide an electron-confiningtunnel. This would make the formation of a relatively stable andsustainable plasma 160 in the space between target and workpiece moredifficult. It has been found that a good minimum working value for thepassed-through flux 116 is about 90-100 Gauss. If the passed-throughflux 116 is too strong and extends much further down than shown, theplasma 160 may enlarge to a point where electrons destructively bombardthe workpiece 150. Neither of the too-weak and too-strong fluxconditions is desirable. In one embodiment, flux intensity just belowthe sputtering surface 120 a should be between 100 Gauss and about 500Gauss or more while flux intensity just above the workpiece top surface152 a/155 a should be less than approximately 20 Gauss.

Ballistic collisions of massive particles such as particle 147 (Ar⁺)with the bottom surface 120 a of the target 120 is desirable howeverbecause they often cause small particles of the target's material tobreak off and move toward the underlying workpiece 150. An example ofsuch an emitted target particle is shown at 149. At the beginning of atarget's life span, the sizes and directions of the emitted targetparticles tend to produce a relatively uniform deposition of the emittedmaterial (e.g., nickel or aluminum) on the top surface (152 a and later155 a ) of the workpiece 150.

Slight nonuniformities in the distribution of magnetic flux lines add upover time however to create nonuniform erosion profiles by the time atarget reaches end life.

FIG. 2A provides a pair of side-by-side cross sectional views designatedas ‘before’ (201) and ‘after’ (202). These before and after views, 201and 202, respectively show the profile of a target's sputtering surface120 a at the start and end of the target's useful life. Line 211represents an axial centerline of the target. Line 212 is a referenceline for noting differences between the before and after conditions.

In the instance of FIG. 2A, the target 210 is composed of aluminum (Al).At the start of its operational life, the aluminum target 210 has anessentially planar sputtering surface 213 as seen on the ‘before’ side201.

At or near the end of its useful life, the aluminum target 210 will havedeveloped a nonplanar sputtering surface 215 characterized by groovessuch as 214, 218 and by hills such as 216. Such grooves (218) and hills(216) tend to undesirably interfere with the edge-to-edge uniformity ofdeposition rate. At some point, the disparity between the target'sgrooves (218) and hills (216) causes too much edge-to-edge variation inthe thickness of the deposited film 155 (FIG. 1), and the eroded targethas to be replaced.

The length of the commercially useful life of a given target may be cutshort by a number of different mechanisms, including by the developmentof a severely nonuniform erosion profile in the sputtering surface ofthe target. Such a cutting short of a target's useful life candisadvantageously increase production costs and increase wastage ofmaterial. Production costs may increase because of the increased numberof times per lot that the production line has to be shut down to replacea target that has reached end-life. Material wastage may be seen asincreasing when the total deposition of a short-lived target is comparedto that of a target life that has a longer production life (e.g., asmeasured in KWhrs). A typical end-life point for a target that is usedin production of semiconductor wafers is when across-the-waferresistivity measurements on deposited metal show an electricalresistivity variation greater than about 5% (3σ) on workpieces producedby the target. If replacement becomes necessary due to a severelynonplanar erosion-profile, the target material that could have beenotherwise sputtered but was not, is considered wasted material.

It is desirable to extend the commercially useful life of each target asmuch as practical so that less target material will be wasted and costof production will be reduced. It is further desirable to extend eachtarget's useful life as much as practical so that replacement frequencyis reduced. Replacement time eats into production time and therebydisadvantageously decreases the workpiece throughput rate of theDC_magnetron PVD system.

Of course, when the severity of a target's grooves (218) and hills (216)becomes too much, such as shown by the end-life profile 215 in the‘after’ portion 202 of FIG. 2A, it becomes necessary to replace thetarget in order to preserve the more-important edge-to-edge depositionuniformity on the workpiece 150 (FIG. 1).

FIG. 2B, like FIG. 2A, also provides a pair of cross sectional viewsdesignated as before (201′) and after (202′) that respectively show theprofile of a target's sputtering surface at the start and end of thetarget's useful life. In the instance of FIG. 2B however, the target 220is composed of a ferromagnetic material such as nickel. Like referencesymbols in the ‘220-229’ number series are used in FIG. 2B instead ofnumbers in the ‘210’ decade of FIG. 2A to denote like elements.

For purposes of comparison, the erosion profile 215 of FIG. 2A is copiedas a dashed curve 215′ into FIG. 2B and placed appropriately relative toinitial reference level 222.

FIGS. 2A and 2B do not represent any specific Al and Ni targets.Instead, these cross section diagrams are provided to explain a specificproblem associated with ferromagnetic targets, namely, acceleratederosion due to de-shunted magnetic flux. This phenomenon is alsosometimes referred to as a ‘pinch-off’.

Note that grooves 224 and 228 of FIG. 2B have sharper, more V-likeappearances than do the counterpart grooves 214 and 218 of FIG. 2A. Notethat groove 224 is shallower than comparative groove 214 (FIG. 2A)relative to the reference level 222/212. Note that the peak ofupside-down hill 226 is closer to reference level 222 than is the peakbottom of counterpart hill 216 relative to its reference line 212. Allthese differences between FIGS. 2A and 2B are believed to be due to thedifference between the nonmagnetic nature of target 210 (FIG. 2A) andthe ferromagnetic nature of target 220 (FIG. 2B).

As parts of the initial sputtering surface 223 of the ferromagnetictarget 220 (FIG. 2B) erode away, target 220 becomes thinner. More of thesourced magnetic flux 115 (FIG. 1) passes through the thinned target aspassed-through flux 116 (FIG. 1) and less is diverted as target-shuntedflux 114. The increased intensity of the passed-through flux 116 altersthe plasma's behavior and generally leads to faster production ofbombardment particles (e.g., 147) in the area of the thinned section.This generally leads to a higher erosion rate at the thinned section.The increased erosion rate of the thinned section in turn generallyleads to a higher, and thus non-uniform, deposition rate in theunderlying area of the workpiece (150 of FIG. 1).

Just as in the case of the nonmagnetic target 210 (FIG. 2A), grooves andhills begin to form in the sputtering surface 223 of the ferromagnetictarget 220 (FIG. 2B). More flux is de-shunted at the grooves than at thehills. This leads to accelerated bombardment at the deepest parts of thegrooves and even faster groove formation at such relatively thinnersections of the target. It also leads to even higher, and thusnon-uniform, deposition rates in the underlying area of the workpiece(150 of FIG. 1).

The sharp V-shaped profile of groove 228 is the end result of thisself-enhancing (run-away) process. Groove 224 is shallower thancounterpart groove 214 because the faster-eroding groove 228 shorten'sthe target's useful lifetime. Hill 226 is taller than counterpart hill216 because the de-shunted magnetic flux of grooves 224 and 228 causesthose grooves to grow faster than counterpart grooves 214 and 218.

As a consequence, the ferromagnetic target 220 (FIG. 2B) generally has asubstantially shorter usable life than its counterpart nonmagnetictarget 210 (FIG. 2A). Edge-to-edge deposition uniformity for theferromagnetic target 220 tends to be worse than that of the counterpartnonmagnetic target 210. The material between erosion profile 225 anddashed counterpart profile 215′ represents additionally wasted materialthat could have been but was not sputtered because of the ferromagneticnature of target 220.

FIG. 3A shows results from experiments performed on an actual pair oflike-shaped aluminum and nickel targets in a same DC_magnetron PVDsystem under essentially same operating conditions (magnet strength ofabout 500 Gauss). Cathode voltage was set at −500V. The Al target had adiameter of 300 mm (millimeters) and an initial thickness of 9 mm. Thenickel target had a diameter of about 200 mm and had an initialthickness of 3 mm (around one third the thickness of the aluminumtarget). Each target was used for sputter depositing material on aseries of like semiconductor wafers (8 inch, pre-oxidized wafers). Theoperating life of the aluminum target was 840 kWH (kilowatt Hours) andwas terminated when greater than 6% (3σ) across-the-wafer resistivityvariation was detected. The deepest groove (100% erosion) was seen atthe 4.55 inch radius (approximately). This deepest groove wasapproximately three-quarters way through the 9 mm thickness of thealuminum target.

The operating life of the nickel target was 105 kWH and was terminatedwith punch-through (100% erosion) at the 4.55 inch radius(approximately).

FIG. 3A plots percent of erosion versus center-to-edge distance with100% erosion at the deepest point of the deepest groove. Since thedeepest groove in the aluminum target had a depth of around 6.8mm,compared to the 3 mm depth of the deepest groove in the Ni target, itshould be appreciated that the Al erosion profile 315 in absolute termsis more than twice as deep as the Ni profile at the 4.55 inch radius. Asseen in FIG. 3A, the erosion profile 325 of the nickel target is spacedbelow the erosion profile 315 of the aluminum target at essentially allradial distances except the 100% erosion point. The area between the twoerosion profiles, 315 and 325, represents a greater relative amount ofwasted material for the nickel sputtering process as compared to thecounterpart aluminum sputtering process. Calculations indicate that lessthan about 20% of the material in the nickel target was consumed beforepinchoff-dictated endlife was reached.

The sharp V-shapes at the deepest parts of nickel grooves 324 and 328supports a conclusion that a pinch-off mechanism was in effect duringthe nickel sputtering process and was hastening end-of-life for thetarget. This is to be contrasted with the smoother shape at the deepestparts of aluminum grooves.

The nickel target that was used for the experiment of FIG. 3A was afirst of five differently-manufactured nickel targets and this firstsample was designated as Sample ‘A’. The other four nickel targets wererespectively designated as Sample ‘B’, ‘C’, and ‘D1’ and ‘D2’.

The five, samples of nickel targets: ‘A’ through ‘D2’ were obtained fromfour different target manufacturing companies (A, B, C, and D) but hadessentially same shapes, including a 3 mm thickness and a 200 mmdiameter. The specific process used by each such target manufacturingcompany is believed to be a trade secret of that company and is notknown to the present inventors. Samples ‘D1’ and ‘D2’ were respectivelyobtained for experimental purposes in the early and late parts of theyear 1997 from Japan Energy Corp. of Japan, which company provided theseexperimental samples in confidential response to specifications providedby the present inventors with shape adaptations made for fitting intothe ‘Applied Materials Endura®’ sputtering tool. Companies A, B, and Csimilarly each provided their respective experimental sample inconfidential response to specifications provided by the presentinventors with shape adaptations made for fitting into the ‘AppliedMaterials Endura®’ sputtering tool.

It may be appreciated from the below, Table 1 characterizations ofsamples ‘A’-‘D2’ that different manufacturing processes where usedbecause each sample demonstrated unique attributes.

It is known in the art that target attributes can vary as a function of:(1) the mine or other source from which metal ore is obtained; (2) thepurification process used for purifying the metal ore (into high puritynickel); (3) the casting process used for melting and recrystallizingthe purified metal; (4) the forging or metal working processes used forshaping the cast metal: (5) the machining processes used for giving eachtarget its final shape; and (6) any annealing or other treatmentsapplied to the target material during manufacture of the target. Assuch, the specific identities of companies A, B and C is irrelevantbecause alternative, target manufacturing processes may be used tocreate targets in accordance with specifications of the presentinvention. Company D is identified herein simply to demonstrate at leastone such company that may create targets in accordance withspecifications set forth herein.

Each of the five, differently-manufactured nickel targets wascharacterized with respect to material purity, texture mix, metal grainsize, magnetic permeability, and initial, average pass-through fluxfactor (%PTF) as indicated by below Table 1. (The initial, average %PTFvalue may not be equal to spot %PTF values present during sputtering.)The last two columns of Table 1 show observed edge-to-edge depositionuniformity on the respective workpieces of each sampled target (asmeasured by resistivity profiling) and the corresponding lifetime(measured in KiloWattHours) for which the stated constraint ondeposition uniformity held true.

Although it is quickly seen that sample ‘D1’ exhibited the bestedge-to-edge deposition uniformity for the longest time (<5% over 90kWHRS) among the five samples, there are lessons to be learned from eachtested sample.

TABLE 1 Ni Texture Mix (percent) TFM Grain Thu-Life Life Sample Purity<111> <113> <200> <220> *** Size μm μ_(max) % PTF Uniformity (3σ)(KW-hrs) A 4N 2.2 11.6 8.1 78.1 20 200 250 14 <10% 20 B 4N8 4 13 16 7757 500 16 55 <10% 60 C 4N 40 28 14 18 8 100 35 45 <10% 3 D1 4N8 9.0 31.832.8 21.6 211 170 50 30 <5% 90 D2 4N8 46 12.73 23.25 16.7 57 130 50 30<5% 50 D1/D2 0.20 2.50 1.41 1.29 1.31 1.00 1.00 1.00 1.80 ** TFM =12*Power(<200>,2.5)/(<111> + <111> + <113><113><220>/20)

In Table 1, the designation 4N means four 9's or 99.99% atomic purity.The designation 4N8 means 99.998% purity. The column at the extremeright labeled “Life” indicates the number of kilowatt hours of operationfor which the uniformity constraint held true. Thus for sample ‘D1’, theuniformity constraint of <5% held true for the first 90 kWHrs ofoperation while for sample ‘D2’ the uniformity constraint of less than5% held true for only 60 kWHrs and became substantially worsethereafter. For each given sample, it is understood that uniformitytends to become worse as usage increases and the erosion profile becomesmore severe. Auto-spacing was used for each tested sample so as toobtain the best possible edge-to-edge deposition uniformity over life asinfluenced by target-to-workpiece spacing.

The initial pass-through flux factor (%PTF) defines what percentage ofthe sourced magnetic flux 115 initially (before erosion) passes throughthe target to define the passed-through flux 116. Initial %PTF isgenerally inversely related to magnetic permeability (μ_(max)) Higherpermeabilities correlate with lower %PTF's and vice versa. %PTF is alsogenerally inversely related to target thickness. Thicker targetscorrelate with lower %PTF's and vice versa. Of course, very thin targets(e.g., much less than 3 mm thick) also correlate with relatively short,commercially-useful lifespans. As such, it is desirable to useferromagnetic targets that are at least 3 mm thick, and preferablythicker, but not so thick as to lower the initial %PTF's below anacceptable range such that it is no longer possible to strike andsustain a plasma.

The double-asterisked (**) row marked as D1/D2 merely provides amathematical division of the results for the respective rows of samplesD1 and D2 . It does not show actual experiment results. Similarly, thetriple-asterisked (***) column marked as TFM merely provides amathematical Texture Figure of Merit calculated as:${TFM} = \frac{12*{{Power}\left( {{\langle 200\rangle},2.5} \right)}}{\left( {{\langle 111\rangle} + {\langle 113\rangle} + {{\langle 111\rangle}{\langle 113\rangle}{{\langle 220\rangle}/20}}} \right)}$

where Power(a,b) means value a raised to the b_th power.

This TFM value does not represent actual experimental results. It does,however correlate roughly with the observed kWHrs (except as applied tosample ‘D2’). The TFM formula is configured in accordance with ourdeduction of a strong, beneficial influence of <200> texture content anda lesser, detrimental influence of the <111> texture and an even lesser,detrimental influence of the <113> texture. Other formulations may bededuced, if desired, from experimental results with larger numbers ofpoints in the characterizing dimensions and use of DOE software analysis(Design of Experiment software).

As seen from the above Table 1, the different manufacturing processesfor respective samples ‘A’ through ‘D2 ’ provided nickel targets withpercent of <200> texture content ranging from as low as about 8% to ashigh as about 33%. The different manufacturing processes also providedexperimental nickel targets with percent of <111> texture contentranging from as low as about 2% to as high as about 46%. The differentmanufacturing processes further provided nickel targets with %PTFranging from as low as 14% to as high as 55% for the same 3 mmthickness. The different manufacturing processes correspondinglyprovided nickel targets with magnetic permeabilities (μ_(max)) rangingfrom as low as 16 to as high as 250. The different manufacturingprocesses additionally provided nickel targets with grain size rangingfrom as low as about 100 μm to as high as about 500 μm.

Thus, it is seen that target characteristics such as texture mix,initial %PTF, magnetic permeability (μ_(max)) and grain size can becontrolled by choice of manufacturing process. The intensity of thesourced magnetic flux 115 in all the experiments described herein was500 Gauss constant. (It is within the contemplation of the invention touse a variable magnetic source that decreases in intensity over timeand/or at spots where thickness is much smaller than at others. Thelatter spots may be identified by recording erosion profiles of a sampletarget over target life time. FIG. 3A is an example of one such erosionprofile.)

Texture mixture is believed to play an important, but notfully-decisive, role in determining target longevity and/or through-lifedeposition uniformity. More specifically, the <200> oriented texture isbelieved to be that which preferentially correlates with longer targetlife and more uniform deposition when such <200> oriented texture isprovided in sufficient quantity. Opposingly, the <111> oriented textureis believed to be that which correlates with shorter target life andless uniform deposition when such <111> oriented texture is provided inexcessive quantity (e.g., above a threshold level of about 10%). To alesser extent, the <113> oriented texture is believed to be that whichcorrelates with shorter target life and less uniform deposition whensuch <113> oriented texture is provided in combination with <111>oriented texture and such <113> oriented texture is provided inexcessive quantity (e.g., above a threshold level of about 13%).

The specific mechanisms at work is not fully understood. The combinationof <111> and <113> oriented texture is believed to be responsible forcausing an undesirable shunting of magnetic flux laterally throughsporadic spots in the target instead of allowing the shunted flux topass-through vertically into the space between target and workpiece.This can lead to nonuniform de-shunting at such sporadic spots, andhence, nonuniform deposition. The detrimental effects of the combinationof <111> and <113> oriented texture may be seen in the results of sample‘C’ as provided by Table 1. Despite good, small grain size (100μm) andrelatively high initial %PTF (45%), sample ‘C’ exhibited the worstresults of all the samples. This is believed to be due in part to thedetrimental effects of the combination of <111> and <113> orientedtextures with respective high percentage values of 40% and 28%.Cold-rolling asymmetry was observed in sample ‘C’. This probably alsocontributed to the poor uniformity and lifespan results of sample ‘C’.

The effect of the <220> texture appears to be one that by itself isneither extremely beneficial nor extremely harmful to determining targetlongevity and/or through-life deposition uniformity. However it may bedetrimental when combined with relatively large quantities of <111> and<113>. It is noted that samples ‘A’ and ‘B’ have roughly same <220>texture content and yet exhibit different lifespan values. Similarly,samples ‘C’ and ‘D2’ have roughly same <220> texture content and yetexhibit different lifespan values.

Before deducing further concepts from Table 1, the experiments whichproduced the results of Table 1 will be examined.

FIG. 3B shows the results of further measurements on the workpiecesproduced by the sample ‘A’ nickel target.

Marker 301 represents the results of uniformity measurements by way of49-point electrical resistivity measurements made on the deposited filmsafter the first 10 kWH of target life. Resistivity variation (whichcorrelates with variation in deposition thickness and/or depositiongranularity of the sputtered-on metal) was about 1.2% for the bulk ofthe 1σ sampling population as seen over the effective edge-to-edge areaof each tested wafer (where ‘effective edge-to-edge area’ does notinclude the peripheral 3 mm exclusion zone). Commercial productionusually requires less than 1.7% thickness variation from effectiveedge-to-edge of deposition among the 1σ bulk portion of the samples (orless than 5% thickness variation among the 3σ primary portion of thesamples). This typical commercial requirement is represented byreference line 310. Useful life of target is measured by the number ofproduction hours (or by kWHrs or by accumulated deposition thickness) ofa given target. In FIG. 3B, useful life of target may be interpreted toend when the deposition uniformity curve crosses upwardly through limitlevel 310 for commercial usability. For the second order approximatingcurve, the limit crossing occurs at about 12 kWHrs in FIG. 3A. At about15 kWHrs, the approximating curve crosses upwardly through the 2.5% (1σ)level, which level is basically equivalent to a 7.5% (3σ) level. Atabout 20 kWHrs, the approximating curve crosses upwardly through the3.3% (1σ) level, which level is basically equivalent to a 10% (3σ)level. At about 30 kWHrs, the approximating curve crosses upwardlythrough the 4.3% (1σ) level, which level is basically equivalent to a13% (3σ) level.

Marker 302 represents the results of uniformity measurements after 30kWH of operation for the same sample ‘A’ target. As seen, the 1σ resultsare substantially in excess of the desired ones whose ceiling is markedby the commercial-usefulness limit, 310.

Marker 303 represents the results of uniformity measurements after 50kWH of operation for the same sample ‘A’ target. As seen, the lavariation results are slightly worse than those for mark 302. Furthermeasurements were taken of workpiece results to punchthrough point 304(105 kWH) but these were essentially flat with the previous results andare therefore not specifically marked off. Visual observations indicatedthat the results probably plateau after mark 303. Second orderinterpolation for the three taken points, 301-303, indicates that thecommercially useful life of the sample ‘A’ target is less than about 12kWH if one wishes to remain under the 1.7% reference line 310. The largefluctuation of edge-to-edge deposition uniformity results, with mostbeing in excess of 5% (3σ) during the lifetime of the sample ‘A’ targetmakes the sample ‘A’ target generally unacceptable for cost-efficient,commercial quality production.

FIG. 4A shows experimental results for the sample ‘B’ target withauto-spacing mimicked. (FIG. 4B shows the underlying T/W spacingexperiments that led to FIG. 4A.) As seen in FIG. 4A from the drawnlines that connect the 3 sample points, the <10% (3σ) line is crossedover at about 45 kWHrs but the results are continuously above 5% (3%)throughout the 60 kWHr test life of the sample ‘B’ target. Over-lifeimprovement in the uniformity value is believed due to development ofhigher %PTF values as target thickness shrinks by consumption. FIG. 4Cshows a surface at the end of the 60 kWHrs use of sample ‘B’ withsignificant sand dune structuring. Large grain size is believed to beresponsible for this nonhomogeneous scarring of the target surface.

FIG. 5A shows a single point experimental result for the sample ‘C’target. The result 501 at 3 kWHrs indicated that subsequent use wouldproduce poorer results because wafer deposition results wereconsistently asymmetric, this indicating that the sample ‘C’ targetpossessed asymmetric cold-working characteristics. This conclusion, thatfurther use of the sample ‘C’ target would produce worse results, isrepresented by the upward-sloping, dash-dot line 502. As seen fromprojection 502, crossing over the <10% (3σ) level is expectedimmediately after about 3 kWHrs of use. FIG. 5B shows the T/W spacingexperiment results at the 3 kWHrs point. The best spacing was around 57mm and the uniformity from other spacings was substantially worse.

FIG. 6A shows experimental results for sample ‘D1’ with auto-spacingagain being mimicked by way of manual adjustment. (Essentially sameresults are expected with autospacing activated.) As seen from the drawnlines that connect the 8 sample points over the 90 kWHr lifespan of thetarget, resistivity remained continuously below the 5% (3σ) levelthroughout the 90 kWHr lifespan of the target. It is seen from this thatcommercially-acceptable nickel sputtering is possible throughout a 90kWHr target life with appropriate adjustment of target characteristics.The overlife, general improvement in deposition uniformity is believedto be due to increasing %PTF values as target thickness shrinks byconsumption. The odd point at 30 kWHrs is probably due to a T/W spacingchange at that time.

FIG. 6B plots target-to-wafer spacing curves relative toacross-the-wafer deposition uniformity for the fourth nickel target(Sample D1). The spacing was controlled manually to locate the minimumvariation points over target life. As seen in FIG. 6B the plottedtarget/wafer spacing optimization curves for sample ‘D1’ include curvesat 10 kWHr (triangle markers), at 20 kWHr (circle markers), at 30 kWHr(solid square markers), at 40 kWH (X markers), at 50 kWHr (X'd trianglemarkers), and at 90 kWHr (hollow square markers), each being relative toobserved edge-to-edge deposition uniformity of the correspondingworkpieces. The best uniformity results were about 5% (3σ) as seen forall curves at a T/W spacing of about 49.5 mm. At the T/W spacing of 57mm, one can see the increasing detrimental effects of operatingrespectively over longer times, from 10 kWHr through 90 kWHr. Less than5% (3σ) operation is seen for the 10-30 kWHr curves at a T/W spacing ofabout 51 mm. Less than 5% (3σ) operation is seen for the 30-90 kWHcurves at a T/W spacing of about 48 mm. Thus commercially-acceptablenickel sputtering is possible throughout a 90 kWHr target life withappropriate adjustment of T/W spacing (to between 51-53 mm in the first20 kWHr of operating life and to between 47-49 mm in the later 30-90 kWHof operating life).

FIG. 7A shows experimental results for the sample ‘D2’ target withauto-spacing again mimicked by manual adjustment. As seen the <5% (3σ)line is crossed over at about 50 kWHrs. FIG. 7B shows the correspondingT/W spacing matrix results for sample ‘D2’.

Referring again to Table 1, a number of conclusions may be drawn.Clearly, the initial value of %PTF alone is not determinative oflifespan below the <5% (3σ) level. This is demonstrated by samples ‘D1’and ‘D2’ having a same %PTF and yet sample ‘D1’ having a lifespan thatis 80% greater than that of sample ‘D2’. The uniformity results ofsample ‘B’ over its 60 kWHrs lifespan is significantly worse than thatof ‘D1’ even though ‘B’ has the highest %PTF value (55%). Sample ‘C’ hasan extremely short lifespan under the <10% (3σ) level even though its%PTF (45%) is the second largest.

On the other hand, sample ‘D1’ has the highest relative amount of <200>texture content and the longest lifespan below the <5% (3σ) levelamongst all the samples. This gives support to the proposition that<200> texture content plays an important, beneficial role in determiningtarget lifetime. Sample ‘C’ has more relative <200> content than sample‘A’ and yet sample ‘A’ has a longer lifespan under the <10% (3σ) level.One difference is that sample ‘A’ has relatively less <111> content.Sample ‘C’ has relatively high content of both <111> and <113> textures.The triple-asterisk column (TFM) appears to define a rough, relativefigure of merit that is applicable to the lifespan under the <10% (3σ)level of samples ‘A’, ‘B’ and ‘C’. It does not work for explaining thedifferent lifespans of samples ‘D1’ and ‘D2’ though.

It appears that texture alone is not determinative of the lifespan anduniformity results. The smaller grain size of ‘D2’ may beneficiallycounter-compensate for its relatively high and detrimental amount of<111> texture content. It may be postulated that a successive series of<111> grains encourage shunting while insertion of <200> or otherwisetextured grains into the series discourages such shunting. The smallerthe grains, the more likely it is that differently textured grains willbe intermixed. Also, small granularity enhances uniform deposition ofnonmagnetic materials.

From the above, a framework of preferences can be worked out. Arelatively large amount of <200> texture is desirable as seen bycomparing sample ‘D1’ against all the other samples. Reduction of theamount of <111> texture is desirable on a second order analysis as seenby comparing sample ‘D1’ against ‘D2’ or by comparing samples ‘A’ and‘B’ against ‘C’. Reduction of the combined amounts of <111> and <113>textures is desirable on a third order analysis as seen by the pooruniformity performance of sample ‘C’. Reduction of grain size is alsodesirable as understood from general workings of sputtering systems. Arelatively large, initial %PTF is desirable as seen by comparing sample‘B’ against samples ‘A’ and ‘C’. Also, it is generally seen in thelifespan plots (e.g., FIGS. 4, 6) that uniformity improves as targetthickness decreases due to material consumption over time. It isunderstood that %PTF increases as thickness decreases. Thus, arelatively large initial %PTF is desirable.

Accordingly, one embodiment in accordance with the present inventionuses a ferromagnetic target having the characteristics of sample ‘D1’ orbetter characteristics (e.g., 3 mm thickness, more <200> content, less<111> content, less <113> content, smaller grains, and/or higher initial%PTF). This embodiment is used in combination with an auto-spacingDC_magnetron PVD system 100 that auto-adjusts T/W spacing 128 (FIG. 1)over target usage life advances so as to obtain the essentially lowestvalues of across-the-wafer uniformity variation. In such an auto-spacingsystem, real-time clock 107 may be used to assist computer 106 with thestep of determining how many kWH's of usage the target 120 hasexperienced. Motor 105 is operated accordingly under control of thecomputer 106 to provide automatic adjustment of the T/W spacing 128 astarget usage life accumulates.

It is alternatively contemplated that a target's erosion life can bemeasured in terms of the sum of the deposition thicknesses on all theworkpieces 150 processed by the given target or an equivalent (e.g.,total number of wafers processed if deposition thickness is essentiallythe same on each). A typical value of total deposition thickness for anickel target might be 400 μm. Accordingly, an alternate embodiment anauto-spacing DC_magnetron PVD system 100 in accordance with the presentinvention that adjusts T/W spacing 128 may use a computer 106 thatcounts the number of wafers processed or sums the measured or predictedthicknesses of deposition of the workpieces 150 processed by the giventarget 120 and automatically adjusts T/W spacing 128 accordingly. Tofind the optimal T/W spacing over life, test runs are performed withfixed T/W settings and then switchover points are selected fromswitching from one T/W setting to another depending on which fixed-T/Wcurve provides the best uniformity at the given period of the target'slifespan.

Table 2 lists some additionally observed characteristics of the sample‘D1’ nickel target.

TABLE 2 Sample D1 Observations Rs uniformity (3σ) <5% (Max-Min)/2thickness <5% uniformity Means Rs (Ωsq) 2.71 at 400 Å Bulk resistivity10.84 μΩ-cm Deposition rate at 1500 W 23 Å/sec power

The present inventors have deduced, as a first order improvement, thatthe <200> texture content of the target should be at least 20% orgreater so as to provide better effective edge-to-edge depositionuniformity. This is evidenced by comparing sample ‘D2’ against thepoorer uniformities of samples ‘A’, ‘B’ and ‘C’. Nickel has aface-centered cubic (FCC) crystal structure similar to that of aluminum.Accordingly, the crystal orientation experience of aluminum is believedtransferable to nickel, with the additional factor that problems imposedby de-shunting of magnetic flux are introduced. A 32% or greater onaverage <200> texture content has been shown to be yet more beneficialfor more uniform deposition as seen by comparing sample ‘D1’ againstsample ‘D2’.

The general results of all of samples ‘A’ through ‘D2’ indicates thatlarger amounts of <200> texture are continuously beneficial, at leastover the range of 8% to about 33% <200> texture. Sample D1 demonstratesthat values of <200> texture content greater than 30% are within reachof current target manufacturing processes. The wide range of <200>texture content in the tested samples suggests that a <200> texturecontent of 35% or greater is within reach of current targetmanufacturing processes. Comparison of sample ‘D1’ and ‘D2’ indicatesthat a roughly one-third decrease in <200> texture content, that isdropping from 32.8% down to 23.3% corresponds with a roughly one-halfdecrease in effective lifespan at the Rs variation constraint of <5%(3σ), that is, from 90 kWHrs down to 50 kWHrs. Thus the beneficialeffects of increasing <200> content appear to be more than linear, andmore so among the samples, appears to provide better than quadraticbenefits.

The present inventors have deduced, as a second order improvement, thatthe <111> texture content of the nickel target should be made as smallas possible (e.g., at least less than 40%, and better yet, less than10%) so as to provide even better effective edge-to-edge depositionuniformity. This is evidenced by comparing the poor performance ofsample ‘C’ (which has 40% <111> content) against the better uniformitiesof samples ‘A’, and ‘B’. This is further evidenced by comparing thepoorer performance of sample ‘D2’ (which has 46% <111> content) againstthe better uniformity of sample ‘D1’ (which has 9% <111> content).Samples ‘A’, ‘B’ and ‘C’ are in one comparable class for the uniformityconstraint of Rs <10% (3σ). Samples ‘D1’ and ‘D2’ are in a secondcomparable class for the uniformity constraint of Rs <5% (3σ).

It is not fully clear what effect <113> content has. The presentinventors postulate, as a third order improvement, that after the <111>texture content of the nickel target has been made as small as possible(e.g., at least less than 40%, and better yet, less than 10%), it may beadvisable to reduce <113> content so as to provide even better effectiveedge-to-edge deposition uniformity. This is evidenced by noting that ofsample ‘C’ (which has 40% <111> content coupled with 28% <113> content)was the poorest performer. Sample ‘D1’ also had high <113> content (ofabout 32%). However, its high <200> content and relatively low <111>content (of about 9%) appear to have countered whatever detrimentaleffect the high <113> content (of about 32%) may have had on depositionuniformity. Nevertheless, it believed preferable to reduce <113>content. High <220> content alone does not appear to be detrimental asevidenced by sample ‘B’ being the best in its class despite its 77%content of <220> textured grains.

Although texture mix appears to be the primary factor for controllingdeposition uniformity, the initial %PTF of the ferromagnetic target(e.g., nickel) should nonetheless be made as large as possible for thegiven thickness class (e.g., 30% or greater for the 3 mm thick nickelclass) so as to minimize variation in across-the-wafer depositionthickness over the target's life due to magnetic pinch-off effect andthe like. Samples ‘B’ through ‘D2’ demonstrate that large initial %PTF'sin the range of 30% or greater are obtainable.

The present inventors have further deduced that metal grain size shouldbe homogeneously less than 150 microns for the bulk of the particles soas to better improve uniformity of deposition. Sample ‘C’ and D2demonstrate that such small grain size is obtainable. It is postulatedthat even smaller grain sizes in the range of about 100 μm to 50 μm orless are within reach of current metal working processes and that suchsmaller grain sizes will provide added benefit. Sample ‘B’ demonstratesthat large grain size may be detrimental to good uniformity even if highvalues of initial %PTF are provided.

The present inventors have further deduced that isotropic working of themetal and essentially complete recrystallization thereafter so as torelieve work-induced strain are also helpful to providing gooduniformity. Sample ‘C’ demonstrates that high %PTF (45%) and small grainsize (100 μm) alone do not guarantee good uniformity (e.g., less than 5%(3σ) variation). This sample, as explained above, appeared to haveasymmetries due to anisotropic working or incomplete recrystallizationsteps.

It is believed that optimal combinations of characteristics forferromagnetic targets can be deduced by understanding how magneticfields are distributed within the DC magnetron system 100 (FIG. 1) afterthe plasma 160 reaches steady state stability, and how this distributionleads to formation of pinch-off V-grooves over time. Higher initial %PTFvalues tend to reduce the rate of pinch-off V-groove formation simplybecause there is less flux to be de-shunted.

A target qualification method in accordance with the present inventiontests supplied targets and proscribes or otherwise removes from usethose which do not meet criteria for grain size, texture content,non-directional working, and %PTF. Metal grain size, and otherworking-induced characteristics may be determined using conventionalmetal characterization techniques. Texture content may be determinedfrom X-ray diffraction analysis. %PTF can be determined by measuringflux intensity at the top and bottom sides of each sample target.Targets from appropriately sampled lots that meet the criteria set forthabove may then be designated as conforming in accordance with acceptedstatistical techniques. Targets from appropriately sampled lots that donot meet one or more of the criteria set forth above should be excludedfrom PVD metal operations.

The above disclosure is to be taken as illustrative of the invention,not as limiting its scope or spirit. Numerous modifications andvariations will become apparent to those skilled in the art afterstudying the above disclosure.

By way of example, although the discussions herein have focused onferromagnetic targets formed from essentially pure Ni (4N or better),nickel alloys such as those of the formulation Ni_(1−x)Si_(x), wherex≦1% which are magnetic and have FCC crystal structures similar toessentially pure Ni are expected to behave similarly in terms ofproviding uniform across-the-wafer deposition.

Given the above disclosure of general concepts and specific embodiments,the scope of protection sought is to be defined by the claims appendedhereto.

What is claimed is:
 1. A method for manufacturing a target adapted forinstallation into a DC_magnetron PVD system wherein said target has adeposition-producing portion composed primarily of an electrically andmagnetically conductive, to-be-deposited metal, said manufacturingmethod comprising the steps of: (a) obtaining a purified form of saidto-be-deposited metal; (b) casting and working the purified metal so asto provide a homogeneous texture mix that is at least 20% <200> texture;(c) further working the cast metal so as to produce a grain size ofabout 200 μm or less; and (d) recrystallizing the further worked metalto uniformly remove work-induced strains.
 2. A method for manufacturinga target according to claim 1 further wherein said casting and workingof the purified metal provides a homogeneous texture mix that is: (b.1)less than 50% in <111> texture content.
 3. A target manufacturing methodaccording to claim 1 wherein said to-be-deposited metal includes nickelas a major component thereof.
 4. A method for manufacturing a targetadapted for installation into a DC-magnetron PVD system wherein saidtarget has a deposition-producing portion composed primarily of amagnetically and electrically conductive, to-be-deposited metal, whichmetal has a tendency to form polycrystals of face-centered cubicstructure, including <200> and <111> textured polycrystals, and saidtarget manufacturing method comprising: (a) providing a supplied metalfor defining said to-be-deposited metal; and (b) working the suppliedmetal so as to provide therein a texture mix that is at least 20% <200>texture and less than about 50% of the <111> texture.
 5. The targetmanufacturing method of claim 4 and further comprising: (c) annealingthe supplied metal so that the post-working texture mix is homogeneouslyat least 20% <200> texture and less than about 50% of the <111> texture.6. The target manufacturing method of claim 4 and further comprising:(c) machining the worked metal so as to provide the machined productwith an initial pass-through flux factor (%PTF) which is large enough toproduce an initial flux for striking plasma.
 7. The target manufacturingmethod of claim 6 wherein said initial pass-through flux factor (%PTF)is about 30% or greater.
 8. The target manufacturing method of claim 6wherein said working and machining cause the post-working and postmachining metal to have a texture mixture having an average value with apredefined per-sample-point restriction of +/−10% or tighter, whereinsaid average value for the texture mixture is at least 20% of the <200>texture and less than 10% of the <111> texture.
 9. The targetmanufacturing method of claim 4 and further comprising: (c) annealingthe supplied metal so that the post-working texture mix is homogeneouslyat least 30% <200> texture.
 10. The target manufacturing method of claim9 wherein said post-working texture mix is at least 32% <200> texture.11. The target manufacturing method of claim 10 wherein saidpost-working texture mix is at least 35% <200> texture.
 12. The targetmanufacturing method of claim 4 and further comprising: (c) machiningthe worked metal so as to provide the machined product an initialthickness that is equal to or greater than about 3 millimeters and withan initial pass-through flux factor (%PTF) of about 45% or greater. 13.The target manufacturing method of claim 12 wherein said initialpass-through flux factor (%PTF) is about 55% or greater.
 14. The targetmanufacturing method of claim 4 wherein said working causes thepost-working metal to have an average or homogeneous grain size of about200 μm or less.
 15. The target manufacturing method of claim 14 whereinsaid working causes the post-working metal to have a homogeneous grainsize of about 150 μm or less.
 16. The target manufacturing method ofclaim 15 wherein said working causes the post-working metal to have ahomogeneous grain size of about 100 μm or less.
 17. The targetmanufacturing method of claim 4 wherein said working causes thepost-working metal to have a homogeneous texture mix that is less than10% of the <111> texture.
 18. The target manufacturing method of claim 4wherein said supplied metal includes nickel as a major componentthereof.
 19. The target manufacturing method of claim 18 wherein saidsupplied metal consists essentially of nickel.
 20. The targetmanufacturing method of claim 4 wherein said supplied metal has atendency to form polycrystals of face-centered cubic structure,including <200>, <111>, <113> and <220> textured polycrystals, and saidworking causes the deposition-producing portion of the target to becharacterized by: (b.1) a texture mixture having an average value with apredefined per-sample-point restriction of +/−10% or tighter, whereinsaid average value for the texture mixture satisfies the Texture Figureof Merit imbalance condition:${57 < {TFM}} = \frac{12*{{Power}\left( {{\langle 200\rangle},2.5} \right)}}{\left( {{\langle 111\rangle} + {\langle 113\rangle} + {{\langle 111\rangle}{\langle 113\rangle}{{\langle 220\rangle}/20}}} \right)}$

 where Power(a,b) means value a raised to the b_th power and saidtexture variables in said TFM equation represent respective percentagesof content of the correspondingly textured polycrystals.
 21. A methodfor manufacturing a target adapted for installation into a DC-magnetronPVD system wherein said target has a deposition-producing portioncomposed primarily of a magnetically and electrically conductive,to-be-deposited metal, which metal has a tendency to form polycrystalsof face-centered cubic structure, including <200> and <111> texturedpolycrystals, and said target manufacturing method comprising: (a)purifying a supplied metal; and (b) working the purified metal so as tothereby provide in the deposition-producing portion of the manufacturedtarget a texture mix that is at least 20% <200> texture and less thanabout 50% of the <111> texture.
 22. The target manufacturing method ofclaim 21 and further comprising: (c) melting and recrystallizing thepurified metal so as to thereby provide in the deposition-producingportion of the manufactured target an average or homogeneous grain sizeof about 200 μm or less.
 23. In a target manufacturing method forproducing a target adapted for installation into a DC-magnetron PVDsystem wherein said target has a deposition-producing portion composedprimarily of a magnetically and electrically conductive, to-be-depositedmetal, which metal has a tendency to form polycrystals of face-centeredcubic structure, including <200> and <111> textured polycrystals, wheresaid target manufacturing method includes the steps of obtaining andworking a purified metal and machining the worked metal, the improvementof adjusting one or more of said obtaining, working and machining stepsso as to cause the deposition-producing portion to be characterized by:(a) a face-centered cubic constituency that has an average orhomogeneous texture mixture that is about 20% or greater of a <200>texture and is less than about 50% of a <111> texture: and (b) aninitial pass-through flux factor (%PTF) which is large enough to producean initial flux for striking plasma.
 24. A method for manufacturing atarget adapted for installation into a DC-magnetron PVD system for useover a target lifetime of at least 60 KiloWatt Hours for producinguniform deposition characterized by 5% (3σ) cross-deposition uniformityor better, wherein said target has a deposition-producing portioncomposed primarily of a magnetically and electrically conductive,to-be-deposited metal, which metal has a tendency to form polycrystalsof face-centered cubic structure, including <200>, <111> and <113>textured polycrystals, and said target manufacturing method comprising:(a) receiving a supplied metal for defining said to-be-deposited metal;and (b) changing the characteristics of the supplied metal so as toprovide therein a substantially uniform texture mix that is at least 30%<200> texture, less than about 10% of the <111> texture and less thanabout 32% of the <113> texture.
 25. The target manufacturing of claim 24wherein: (b.1) said changing causes the <113> texture content to be lessthan about 28%.
 26. The target manufacturing of claim wherein: (b.1)said changing causes the <200> texture content to be at least about 32%.27. The target manufacturing of claim 24 and further comprising: (c)changing the characteristics of the supplied metal so as to provide themanufactured target with an initial, through-target pass-through fluxfactor (%PTF) of at least about 30%.
 28. The target manufacturing ofclaim 27 and further comprising: (c) changing the characteristics of thesupplied metal so as to provide the manufactured target with ahomogeneous grain size of about 200 μm or less.